1. Field of the Invention
The present invention relates to a magnetic head and, in particular, to a magnetic head with an improved flexible cable junction structure.
2. Description of the Related Art
The general construction of a magnetic head used in a conventional hard magnetic disk device will be described with reference to FIG. 4. A load beam 21, which consists of a stainless steel plate, comprises a rectangular base portion 21a situated at the rear end thereof, a flat portion 21c connected to the base portion 21a through two elastic portions 21b and extending to the forward end, and a protruding portion 21d outwardly protruding from one side of the base portion 21a and situated in the same plane as the base portion 21a. There is provided on either side of the flat portion 21c a bent portion 21e bent downward. A rectangular mount 23 consisting of a stainless steel plate is superimposed on the portion of the upper surface of the base portion 21a excluding the protruding portion 21d and is fastened thereto by spot welding or the like. Formed at the center of the mount 23 and the base portion 21a, which are superimposed one upon the other, is a through-hole 24 for mounting the magnetic head to a drive arm (not shown) of a hard magnetic disk device.
A flexure 25, which consists of a thin stainless steel plate and which is flexible, comprises a wide portion 25a extending over the central portion of the upper surface of the flat portion 21c of the load beam 21 from the forward end toward the rear end thereof, a narrow portion 25b passing between the two elastic portions 21b of the load beam 21 and extending around the outer periphery of the base portion 21a, and an end portion 25c superimposed on the upper surface of the protruding portion 21d of the load beam 21.
As shown in FIG. 5, a slider 27 consisting of a ceramic and substantially formed as a parallelepiped is fastened to a tongue 25d provided at the forward end of the flexure and partially cut away. On the forward end surface 27a of the slider 27, a thin-film head element 28 for recording and reproducing information on and from a hard magnetic disk and four connection terminals 29 connected to the head element 28 are formed by a thin-film formation technique. Of the four connection terminals 29, two serve to transmit recording signals and the other two serve to transmit reproduction signals.
A ground layer 30 consisting of an insulator such as polyimide is provided around the wide portion 25a and on the narrow portion 25b and the end portion 25c of the flexure 25. Formed on the ground layer 30 are four conductive patterns 31 consisting of nickel- and gold-plated copper.
At the end surface 27a of the slider 27, the forward ends of the four conductive patterns 31 are connected to the connection terminals 29 through balls 32 consisting of a conductive material such as Au. Of the four conductive patterns 31, two are for recording and the other two are for reproduction according to the functions of the connection terminals 29.
As shown in FIG. 6, on the end portion 25c of the flexure 25, the width of the conductive patterns 31 is enlarged such that their end portions are rectangular, forming four rectangular pads 31a, which are arranged in a row from the front side of the flexure 25.
The conductive patterns 31 are covered with an insulating layer (not shown) consisting of polyimide resin or the like. However, the end portions of the conductive patterns 31 connected to the connection terminals 29 of the head element 28 and the portions thereof on the end portion 25c of the flexure 25 are not covered with an insulating layer, the pads 31a being exposed on the end portion 25c. 
A flexible cable 33 comprises an insulating substrate 33a consisting of polyimide resin or the like, four conductors 33b formed thereon and consisting of copper or the like, and an insulating covering sheet 33c covering the conductors 33b. The end portions of the conductors 33b are formed as round bumps 33e whose surfaces are solder-plated so as to make it possible to perform soldering connection. The bumps 33e are formed in a row from the front side. From the end portion 33d of the flexible cable 33, which is superimposed on the end portion 25c of the flexure 25, the covering sheet 33c is removed, so that the surfaces of the bumps 33e are exposed.
The bumps 33e and the pads 31a are joined to each other by pressurizing and heating, with the solder-plated surfaces of the bumps 33e and the gold-plated surfaces of the pads 31a being opposed to each other. A round through-hole 34 provided in the protruding portion 21d and a through-hole 35 provided at the end of the flexible cable 33 are used as a means of positioning for the bumps 33e and the pads 31a when they are superimposed one upon the other. The round bumps 33e are included in the rectangular pads 31a. 
The flexible cable 33 is led out rearward from the end portion 25c of the flexure 25 and connected to the main body of the hard magnetic disk device, serving to transmit recording and reproduction signals to the thin-film head element 28.
The above magnetic head is mounted to a driving arm of a hard magnetic disk device (not shown) by attaching the mount to the driving arm such that the upper surface 27b of the slider 27 is opposed to the magnetic recording surface of the magnetic disk. During operation, the slider 27 fixed to the flexure 25 flies over the magnetic recording surface of the magnetic disk at a predetermined distance, and magnetic recording and reproduction are performed on and from the magnetic disk by the head element 28, with the airflow being followed due to the flexibility of the flexure 25.
When the flexible cable 33 led out of the conventional magnetic head is deflected during assembly, etc., great distortion occurs to the junction, in particular, between the bumps 33e and the pads 31a which junction is nearest to the lead-out side of the flexible cable 33, causing breakage to the junction, with the result that the exchange of information between the head element 28 and the cable 33 is interrupted.
The present invention has been made with a view toward solving the above problem. Accordingly, it is an object of the present invention to make it possible to prevent occurrence of distortion to the junctions between the bumps 33e and the pads 31a. 
To achieve the above object, there is provided, in accordance with the present invention, a magnetic head comprising a flexure having conductive patterns formed thereon, a flexible cable having conductors, a head element provided at the forward end of the flexure and connected to the conductive patterns, pads provided at the rear end of the flexure and connected to the conductive patterns, a dummy pad provided at the rear end of the flexure and not connected to the conductive patterns, bumps provided at the forward end of the flexible cable and adapted to transmit electric signals between the head element and the flexible cable, a dummy bump provided at the forward end of the flexible cable and not adapted to transmit electric signals between the head element and the flexible cable, wherein the forward-end portion of the flexible cable is superimposed on the rear-end portion of the flexure to effect junction between the pads and the bumps and between the dummy pad and the dummy bump, the junction between the dummy pad and the dummy bump being positioned nearer to the flexible cable lead-out side than the junctions between the pads and the bumps.
Further, the dummy bump is not connected to the conductors of the flexible cable.
Furthermore, the area of junction between the dummy bump and the dummy pad is larger than the area of junction between each bump and each pad.
Furthermore, the dummy pad and the dummy bump are formed of the same materials as those of the pads and the bumps.
Furthermore, the height of the junction portion between the dummy pad and the dummy bump is the same as that of the junction portions between the pads and the bumps.